JP2019214659A - Ink for forming functional layer - Google Patents

Abstract

To provide an ink for forming a functional layer extremely small in dry unevenness between pixels and capable of achieving function originally obtained by a functional material sufficiently.SOLUTION: There is provided an ink for forming a functional layer in which 1) solvents (B) and (C) have Hansen solubility parameter δP<10 and δH<9, 2) a first solvent or dispersant (B) is a solvent containing an aromatic ring, and having boiling point at ordinary pressure of 250 to 310°C, 3) a second solvent (C) is a solvent having boiling point at ordinary pressure 160°C to boiling point of the first solvent (B) used in 1 or lower, and 4) the second solvent (C) is used to be over the same amount of used amount of the first solvent or dispersant (B) when total used amount of the first solvent (B) and the second solvent (C) is 100 part.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink for forming a functional layer.

  In order to obtain a coating film containing a functional material, a technique of mixing the functional material described above with a solvent or a dispersion medium, applying the mixture to a substrate such as a support, and removing the solvent or the dispersion medium is often used. ing. As the functional material at this time, a dye, a pigment, a semiconductor material, an organic EL, a quantum dot, a conductive material, an insulating material, and the like are appropriately selected and used for the purpose of obtaining a desired function. Recently, light-emitting elements using organic EL, quantum dots, and the like as display materials have been receiving attention.

  For example, various light emitting devices usually include an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode. When an electric field is applied to the light-emitting element, holes are injected from the anode into the hole transport layer, electrons are injected from the cathode into the electron transport layer, and then holes and electrons are injected into the light-emitting layer. In the light emitting layer, the injected holes and electrons are recombined, and the energy generated at this time causes the light emitting material in the light emitting layer to emit light. Note that the light-emitting element does not have a hole-transport layer and / or an electron-transport layer in some cases. Further, another layer such as a hole injection layer and an electron injection layer may be included.

  The self-luminous element is suitable from the viewpoint that the display can be reduced in weight and thickness in addition to display performance such as high visibility and little dependency on a viewing angle, and is being put to practical use. However, since improvement in power consumption is still required, research for further improvement in luminous efficiency is ongoing.

  Various solvents are used for such a functional layer forming ink. For example, Patent Documents 1 to 3 disclose using a solvent similar to that used in the present invention to prepare an ink and form a functional layer. Is going.

  Patent Document 1 describes that an ink can be prepared using a diphenyl ether derivative or a naphthalene derivative as an organic solvent having a boiling point of 180 ° C. or more at normal pressure. Patent Literature 2 discloses that 3-methyldiphenyl ether (3-phenoxytoluene) can be used in an ink containing at least a diphenyl ether derivative as an organic solvent.

  Further, Patent Literature 3 describes that as an ink using a combination of different organic solvents, an ink can be prepared by combining 1-methylnaphthalene and cyclohexylbenzene.

JP 2017-193618 A JP 2006-241309 A WO2013 / 046264A1

  In recent years, from the viewpoint of enabling high-definition patterning and high material use efficiency, formation of each layer constituting an organic light-emitting element by a wet film formation method, particularly, an inkjet method has been studied.

In this wet film forming method, a substrate provided with a bank structure is used to arrange ink at an intended position (pixel). Ink ejected to pixels located at the side edges of the substrate tends to dry faster than ink ejected to pixels located at the center of the substrate. This is because in the center of the substrate, there are many ink solvent molecules that evaporate because each pixel is adjacent to each other, but the pixels located around the substrate have less ink solvent molecules that evaporate and the center of evaporation Because it is faster than the part. As described above, if the drying time of the ink filled in the pixel differs depending on the position of the pixel in the substrate, unevenness in the thickness of the light emitting layer formed based on the ink between the pixels in the substrate occurs. When there is such film thickness unevenness, a difference occurs in the current flowing through the light emitting layer and the like, which causes display unevenness such as uneven brightness and uneven emission color when the light emitting layer emits light.

  For example, in each of the inks of Patent Literatures 1 and 2, there is no description about the mixture ratio of a plurality of solvents assuming that they are used in combination. However, even if it is attempted to exert the uniformity, the drying state differs between the side end portion and the central portion, and drying unevenness occurs. As a result, uneven distribution of the functional material occurs, and functional unevenness sometimes occurs. On the other hand, in the ink of Patent Document 3, although it is suggested that 1-methylnaphthalene and cyclohexylbenzene are combined, since the boiling points of both are close to each other, the drying of the side end proceeds more quickly. Again, uneven drying occurs, resulting in uneven distribution of the functional material and uneven function.

  Accordingly, the present invention provides, as an ink using a functional material, an ink for forming a functional layer, in which unevenness in drying between pixels is extremely small and the functional material itself can fully exhibit its inherent function. Aim.

  The present inventors have conducted intensive research in order to solve the above problems. As a result, the present inventors have found that the above problem can be solved by using two or more different kinds of solvents or dispersion media having a specific Hansen solubility parameter in a specific ratio as a solvent or dispersion medium, and completed the present invention. It led to.

That is, the present invention relates to an ink for forming a functional layer, comprising a functional material (A) and at least a first solvent or dispersion medium (B) and a second solvent or dispersion medium (C).
1) Both the solvents or dispersion media (B) and (C) have Hansen solubility parameters δP <10 and δH <9,
1) The first solvent or dispersion medium (B) is a solvent or dispersion medium containing an aromatic ring and having a boiling point of 250 to 310 ° C. at normal pressure;
2) The second solvent or the dispersion medium (C) is a solvent or a dispersion medium having a boiling point at normal pressure of 160 ° C. to the boiling point of the first solvent or the dispersion medium (B) used in 1 above,
3) When the total amount of the first solvent or the dispersion medium (B) and the second solvent or the dispersion medium (C) is 100 parts by mass, the second solvent or the dispersion medium (C) It was used so as to exceed the same amount as the amount of one solvent or dispersion medium (B),
It is intended to provide an ink for forming a functional layer, characterized in that:

  According to the present invention, when a functional layer is formed with an ink containing a functional material, unevenness in drying between a side end portion and a central portion is extremely small, and the function inherent in the functional material itself is provided on the entire surface. It is possible to obtain an ink for forming a functional layer that can be fully utilized.

FIG. 3 is a partial cross-sectional view schematically illustrating a step of forming a coating film by an inkjet printing method.

  Hereinafter, embodiments for carrying out the present invention will be described in detail.

[Functional layer forming ink]
The ink for forming a functional layer according to the present embodiment has a Hansen solubility parameter δP (dispersion term) <10 and δH (hydrogen bond term) <9 as the functional material and the first solvent or dispersion medium (B), An organic solvent containing an aromatic ring and having a boiling point of 250 to 310 ° C. at normal pressure is used. As a second solvent or a dispersion medium (C), a Hansen solubility parameter δP (dispersion term) <10 and δH (hydrogen bond term) <9, including an organic solvent having a boiling point of 160 ° C. at normal pressure or lower than the boiling point of the first solvent or the dispersion medium (B) used above, and containing the former solvent or the dispersion medium in a specific ratio. The biggest feature. Hereinafter, the first solvent or the dispersion medium (B) may be abbreviated as the solvent (B), while the second solvent or the dispersion medium (C) may be abbreviated as the solvent (C).

  The functional material will be described in detail later, but in the case of applying the ink for forming a functional layer of the present invention to a display display application, the functional material contained therein is typically a luminescent material. . The functional material may further include a light-emitting material and, if necessary, additives and the like. In this specification, “light emission” includes light emission by fluorescence and light emission by phosphorescence.

  In the ink of the present invention, as the functional material (A), one or two or more known and commonly used functional materials can be used. Specific examples of such a functional material (A) include the following.

<Functional materials>
Examples of the functional material include dyes, pigments, semiconductor materials, organic ELs, quantum dots, conductive materials, and insulating materials.

[dye]
Dyes as the functional material include 4-dicyanmethylene-2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM), coumarin, pyrene, perylene, rubrene, derivatives thereof, Or any combination thereof.

[Quantum dots]
Quantum dots as functional materials have a diameter of less than 150 °. The population of quantum dots has an average diameter in the range of 15 ° to 125 °. The quantum dots may be spherical, rod-shaped, disc-shaped, or other shapes. Quantum dots can include a core of semiconductor material. A quantum dot can include a core having the formula MX, where M is cadmium, zinc, magnesium, mercury, aluminum, gallium, indium, thallium, or a mixture thereof, and X is oxygen, sulfur, Selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, or a mixture thereof.

[Organic EL]
The organic EL as a functional material includes a light emitting material and a host material.

[Organic EL red light-emitting material]
The red light emitting material is not particularly limited, and various red fluorescent materials and red phosphorescent materials can be used alone or in combination of two or more.

  The red fluorescent material is not particularly limited as long as it emits red fluorescence. For example, a perylene derivative, a europium complex, a benzopyran derivative, a rhodamine derivative, a benzothioxanthene derivative, a porphyrin derivative, Nile Red, 2- (1, 1-dimethylethyl) -6- (2- (2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H-benzo (ij) quinolinidin-9-yl) ethenyl)- 4H-pyran-4H-ylidene) propanedinitrile (DCJTB), 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM), poly [2-methoxy-5 -(2-ethylhexyloxy) -1,4- (1-cyanovinylenephenylene)], poly [{9,9-dihexyl-2,7-bi (1-cyanovinylene) fluorenylene {ortho-co- {2,5-bis (N, N'-diphenylamino) -1,4-phenylene}], poly [{2-methoxy-5- (2-ethylhexyloxy) ) -1,4- (1-cyanovinylenephenylene)}-co- {2,5-bis (N, N′-diphenylamino) -1,4-phenylene}] and the like.

  The red phosphorescent material is not particularly limited as long as it emits red phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium, and among the ligands of these metal complexes, At least one has a phenylpyridine skeleton, a bipyridyl skeleton, a porphyrin skeleton, or the like. More specifically, tris (1-phenylisoquinoline) iridium, bis [2- (2′-benzo [4,5-α] thienyl) pyridinate-N, C3 ′] iridium (acetylacetonate) (btp2Ir (acac )), 2,3,7,8,12,13,17,18-octaethyl-12H, 23H-porphyrin-platinum (II), bis [2- (2′-benzo [4,5-α] thienyl) Pyridinate-N, C3 '] iridium and bis (2-phenylpyridine) iridium (acetylacetonate).

  Further, the red light emitting layer may contain a host material to which the red light emitting material is added as a guest material, in addition to the red light emitting material described above.

  The host material recombines holes and electrons to generate excitons and transfers the energy of the excitons to the red light-emitting material (Forster or Dexter transfer) to excite the red light-emitting material. Having. When such a host material is used, for example, a red light-emitting material that is a guest material can be used by doping the host material as a dopant.

  Such a host material is not particularly limited as long as it exhibits the function as described above for the red light-emitting material to be used. For example, an acene derivative (acene derivative) such as a naphthacene derivative, a naphthalene derivative, or an anthracene derivative may be used. Materials), distyrylarylene derivatives, perylene derivatives, distyrylbenzene derivatives, distyrylamine derivatives, quinolinolato-based metal complexes such as tris (8-quinolinolato) aluminum complex (Alq3), and tria such as tetramers of triphenylamine. Reelamine derivative, oxadiazole derivative, silole derivative, carbazole derivative, biscarbazole derivative, indolocarbazole derivative, oligothiophene derivative, benzopyran derivative, triazole derivative, benzoxazole derivative, benzothiazole Derivatives, quinoline derivatives, 4,4'-bis (2,2'-diphenylvinyl) biphenyl (DPVBi) and the like, may be used singly or in combination of two or more of them.

[Organic EL blue light-emitting material]
Examples of the blue light emitting material include various blue fluorescent materials and blue phosphorescent materials, and one or a combination of two or more of them can be used.

  The blue fluorescent material is not particularly limited as long as it emits blue fluorescence.For example, distyrylamine derivatives such as distyryldiamine-based compounds, fluoranthene derivatives, pyrene derivatives, perylene and perylene derivatives, anthracene derivatives, Oxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, chrysene derivatives, phenanthrene derivatives, distyrylbenzene derivatives, tetraphenylbutadiene, 4,4′-bis (9-ethyl-3-carbazovinylene) -1,1′-biphenyl (BCzVBi ), Poly [(9.9-dioctylfluorene-2,7-diyl) -co- (2,5-dimethoxybenzene-1,4-diyl)], poly [(9,9-dihexyloxyfluorene-2, 7-diyl) -ortho-co- (2-me Xy-5- {2-ethoxyhexyloxy} phenylene-1,4-diyl)], poly [(9,9-dioctylfluorene-2,7-diyl) -co- (ethylnylbenzene)] and the like. .

  The blue phosphorescent material is not particularly limited as long as it emits blue phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. , 6-Difluorophenylpyridinate-N, C2 ']-picolinate-iridium, tris [2- (2,4-difluorophenyl) pyridinate-N, C2'] iridium, bis [2- (3,5-tri Fluoromethyl) pyridinate-N, C2 ']-picolinate-iridium, bis (4,6-difluorophenylpyridinate-N, C2') iridium (acetylacetonate) and the like.

The blue light emitting layer may contain a host material to which the blue light emitting material is added as a guest material, in addition to the blue light emitting material described above.

  As such a host material, the same host material as that described for the red light-emitting layer can be used.

  As the host material of such a blue light emitting layer, it is preferable to use an acene derivative (acene-based material), like the host material of the red light emitting layer. This allows the blue light emitting layer to emit red light with higher luminance and higher efficiency.

[Organic EL green light-emitting material]
The green light-emitting material is not particularly limited, and includes, for example, various green fluorescent materials and green phosphorescent materials, and one or more of these can be used in combination.

  The green fluorescent material is not particularly limited as long as it emits green fluorescence. For example, quinacridone such as coumarin derivatives and quinacridone derivatives and derivatives thereof, 9,10-bis [(9-ethyl-3-carbazole)- Vinylenyl] -anthracene, poly (9,9-dihexyl-2,7-vinylenefluorenylene), poly [(9,9-dioctylfluoren-2,7-diyl) -co- (1,4-diphenylene-vinylene) -2-methoxy-5- {2-ethylhexyloxy} benzene)], poly [(9,9-dioctyl-2,7-divinylenefluorenylene) -ortho-co- (2-methoxy-5- (2 -Ethoxylhexyloxy) -1,4-phenylene)] and the like.

  The green phosphorescent material is not particularly limited as long as it emits green phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. 2-phenylpyridine) iridium (Ir (ppy) 3), bis (2-phenylpyridinate-N, C2 ') iridium (acetylacetonate), fac-tris [5-fluoro-2- (5-trifluoro) Methyl-2-pyridine) phenyl-C, N] iridium and the like.

  Further, in addition to the above-described green light-emitting material, the green light-emitting layer may include a host material using the green light-emitting material as a guest material.

  As such a host material, the same host material as that described for the red light-emitting layer can be used.

  As the host material for such a green light-emitting layer, it is preferable to use an acene derivative (acene-based material), like the host material for the red light-emitting layer. This allows the green light emitting layer to emit red light with higher luminance and higher efficiency.

  Further, the host material of the green light emitting layer is preferably the same as the host material of the blue light emitting layer described above. Thereby, in both light emitting layers, green light and blue light can be emitted with good balance.

  The molecular weight of the light emitting material is preferably 5000 g / mol or less, more preferably 2000 g / mol or less, and even more preferably 300 to 2000 g / mol. It is preferable that the molecular weight of the host material be 5000 g / mol or less because the light-emitting material can be easily dissolved in a solvent.

  The content of the luminescent material as the functional material is preferably from 0.1 to 50% by mass, and more preferably from 0.1 to 10% by mass, based on the mass of the host material. When the content of the light emitting material is 0.1% by mass or more, a uniform film can be formed. On the other hand, when the content of the light-emitting material is 10% by mass or less, it is preferable because a decrease in light-emitting efficiency due to concentration quenching of the light-emitting material can be suppressed.

[Solvent or dispersion medium]
In one embodiment, the solvent or dispersion medium applied to the ink for forming a functional layer of the present invention is a different solvent of the solvent (B) and the solvent (C). In the present invention, the solvent (B) and the solvent (C) are determined using the Hansen solubility parameter as one index. The Hansen solubility parameter is obtained by dividing a solubility parameter introduced by Hildebrand into three components, δD, δP, and δH, and expressing it in a three-dimensional space. δD indicates an effect by nonpolar interaction, δP (dispersion term) indicates an effect by dipole force, and δH (hydrogen bonding term) indicates an effect by hydrogen bonding force. Hansen solubility parameter values for various monomers are described, for example, in Charles M. et al. The Hansen solubility parameter values of monomers not described in “Hansen Solubility Parameters: A Users Handbook” by Hansen or the like can be calculated using computer software (HSPiP which can be calculated by Hansen Solubility Parameters in Practice). .

  The present invention is characterized in that a solvent is selected by focusing on δP (dispersion term) and δH (hydrogen bond term). As described above, as the solvent (B), an organic solvent having a Hansen solubility parameter δP (dispersion term) <10 and δH (hydrogen bond term) <9, containing an aromatic ring, and having a boiling point of 250 to 310 ° C. at normal pressure. On the other hand, the solvent (C) has a Hansen solubility parameter δP (dispersion term) <10 and δH (hydrogen bond term) <9, and a boiling point at normal pressure of 160 ° C. to the first used above. An organic solvent having a boiling point of the solvent or the dispersion medium (B) or lower.

  The solvent or dispersion medium is not particularly limited, but is appropriately selected from known ones depending on the functional material to be included in the layer to be formed, and the total amount of the solvent (B) and the solvent (C) is determined by mass. The solvent (C) is used so as to exceed the same amount as the amount of the solvent (B) when converted to 100 parts.

  In the ink for forming a functional layer of the present invention, the solvent (C) is used such that the usage ratio of the solvent (B) to the solvent (C) is not less than the usage amount of the solvent (B). Above all, when the total amount of the solvent (B) and the solvent (C) is 100 parts by mass in terms of mass, the amount of the solvent (C) is more than 50 parts, which is more excellent in the effect of suppressing drying unevenness. In particular, it is preferable to set the ratio of solvent (B) / solvent (C) to 40/60 to 15/85 because the effect of suppressing unevenness in drying between pixels is most excellent.

  In preparing the ink for forming a functional layer of the present invention, other organic solvents that do not fall under the solvents (B) and (C) are used as long as the technical effects of using the solvents (B) and (C) together are not impaired. A solvent can be used in combination.

  The solvent (B) and the solvent (C) may be selected one by one and used in combination, or two or more kinds may be selected and used in combination. Further, as long as the solvent (B) or the solvent (C) satisfies the above definition, it is preferable that each of them has a lower boiling point because drying becomes easier.

  Depending on the functional material (A) to be used, one or both of the solvent (B) and the solvent (C) may function as a solvent, or may function as a dispersion medium. However, if the solvent (B) or the solvent (C) is selected from those that dissolve the functional material (A), the original function of the functional material is reduced. Ink that can enhance the stability of the ink without the use of potential surfactants or dispersion stabilizers, and has excellent uniformity of the functional material in the coating film containing the functional material in finer areas It is more preferable because it is possible.

  As the solvent (B) in the present invention, specifically, diphenyl ether (boiling point: 258 ° C., δP = 3.4, δH = 4.0), 1-ethylnaphthalene (boiling point: 260 ° C., δP = 2.8, δH = 3.8), 2-isopropylnaphthalene (boiling point 268 ° C, δP = 2.2, δH = 3.0), 1-methoxynaphthalene (boiling point 271 ° C, δP = 4.6, δH = 5.6), 3-phenoxytoluene (boiling point 272 ° C., δP = 3.5, δH = 3.6), 2-methoxybiphenyl (boiling point 274 ° C., δP = 4.2, δH = 5.0), 2-ethoxynaphthalene (boiling point 282 ° C, δP = 4.3, δH = 5.0), 1-ethoxynaphthalene (boiling point 282 ° C, δP = 4.3, δH = 5.0), 3,3′-dimethylbiphenyl (boiling point 282 ° C, δP = 1.9, δH = 1.8), 3-ethylbiphe Le (boiling point 284 ℃, δP = 1.9, δH = 2.3) and 4-isopropyl-biphenyl (boiling point 291 ℃, δP = 1.9, δH = 2.2) and the like can be given.

  Among them, from the viewpoint of the solubility of the solute, the solvent (B) may be 1-ethylnaphthalene, 2-isopropylnaphthalene, 1-methoxynaphthalene, 2-methoxybiphenyl, 2-ethoxynaphthalene, 1-ethoxynaphthalene, At least one solvent or dispersion medium selected from the group consisting of 3,3'-dimethylbiphenyl, 3-ethylbiphenyl and 4-isopropylbiphenyl is more preferred.

  On the other hand, as the solvent (C) in the present invention, specifically, mesitylene (boiling point: 164 ° C., δP = 0.6, δH = 0.6), diethylene glycol isopropyl methyl ether (boiling point: 179 ° C., δP = 4.6) , ΔH = 4.9), indane (boiling point 179 ° C, δP = 3.3, δH = 3.3), methyl benzoate (boiling point 200 ° C, δP = 8.2, δH = 4.7), pentanoic acid Amyl (boiling point 205 ° C, δP = 3.3, δH = 4.5), ethyl levulinate (boiling point 205 ° C, δP = 7.8, δH = 6.8), tetralin (boiling point 207 ° C, δP = 2. 0, δH = 2.9), ethyl octanoate (boiling point 208 ° C., δP = 3.8, δH = 4.4), butyl phenyl ether (boiling point 210 ° C., δP = 3.5, δH = 4.1) , Ethyl benzoate (boiling point 212 ° C, δP = 6.2, δH = 6.0 , Diethylene glycol butyl methyl ether (boiling point 212 ° C, δP = 4.6, δH = 5.1), propylanisole (boiling point 215 ° C, δP = 4.0, δH = 4.0), isopentyl benzoate (boiling point 218 ° C) , ΔP = 5.5, δH = 3.3), butyl benzyl ether (boiling point 220 ° C, δP = 3.1, δH = 3.6), amyl hexanoate (boiling point 226 ° C, δP = 3.1, δH) = 4.4), methyl-p-toluate (bp 223 ° C, δP = 6.5, δH = 3.8), methylacetophenone (boiling point 226 ° C, δP = 6.7, δH = 4.0), hexyl Benzene (boiling point 226 ° C., δP = 1.9, δH = 4.0), isoamyl hexanoate (boiling point 226 ° C., δP = 2.9, δH = 4.0), dihexyl ether (boiling point 226 ° C., δP = 3) 2.0, δH = 2.8), methyl -O-anisate (boiling point 228 ° C., δP = 8.3, δH = 5.3), nonyl acetate (boiling point 228 ° C., δP = 3.2, δH = 4.3), methyl decanoate (boiling point 229 ° C., δP = 3.3, δH = 4.4), diethyl glutarate (boiling point 230 ° C., δP = 7.0, δH = 7.8), propyl benzoate (boiling point 230 ° C., δP = 5.7, δH = 3.6), heptylbenzene (boiling point 235 ° C., δP = 1.9, δH = 2.5), cyclohexylbenzene (boiling point 236 ° C., δP = 1.7, δH = 2.6), ethyl acetophenone (boiling point 239) ° C, δP = 6.3, δH = 3.6), methyl naphthalene (boiling point 241 ° C, δP = 0.8, δH = 4.7), hexyl hexanoate (boiling point 244 ° C, δP = 3.0, δH = 4.1), diethylene glycol butyl ether acetate (boiling point 2 7 ° C., δP = 4.1, δH = 8.2), diethyl dipropylmalonate (boiling point 249 ° C., δP = 3.0, δH = 4.2), butyl benzoate (boiling point 250 ° C., δP = 5) 6, δH = 5.5), diethylene glycol diacetate (boiling point 250 ° C, δP = 6.4, δH = 8.4), 2-ethylnaphthalene (boiling point 252 ° C, δP = 2.8, δH = 3. 8), butyl O-butyryl lactate (boiling point 252 ° C., δP = 4.0, δH = 5.6), diisopropyl adipate (boiling point 253 ° C., δP = 3.8, δH = 4.7), diethylene glycol di Butyl ether (boiling point 255 ° C., δP = 4.7, δH = 4.4), ethyl p-anisate (boiling point 257 ° C., δP = 7.2, δH = 5.1), isopentyl benzoate (boiling point 262 ° C., δP = 4.8, δH = 3.2), dihept Toluene (boiling point 262 ° C, δP = 2.7, δH = 2.6), octylbenzene (boiling point 264 ° C, δP = 1.5, δH = 2.2), hexyl benzoate (boiling point 272 ° C, δP = 5) 0.0, δH = 3.4), dipropyl adipate (boiling point 274 ° C, δP = 4.0, δH = 5.2), nonylbenzene (boiling point 282 ° C, δP = 1.4, δH = 2.2) And dodecylbenzene (boiling point 288 ° C., δP = 1.1, δH = 1.8) and the like. These solvents (C) may be used alone or in combination of two or more.

  When the solvent (B) and the solvent (C) both have the above-mentioned ranges in δP and δH, a residual solvent is generated irrespective of the boiling point. For example, a luminescent material may be used as the functional material (A). When the functional layer forming ink used is prepared, the luminous efficiency of the light emitting element obtained therefrom may be insufficient, which is not preferable.

  Further, when the solvent (B) and the solvent (C) are less than the above range in boiling point, when forming the functional layer in a planar shape, the volatility at the side end portion is higher than at the center portion, and drying unevenness is caused. This is likely to occur, and it is difficult to dry the applied functional layer forming ink uniformly over the entire surface including the central portion and the side edges. In addition, rapid drying will cause precipitation of the functional material (A) when the functional material (A) is a substance that is easily crystallized. This precipitate is likely to occur and the flow of electrons is obstructed, so that a difference in luminance at the time of light emission can be caused by a portion such as a central portion and a side edge portion in the planar light emitting layer, or the luminous efficiency of the display element is insufficient. It is not preferable because it may occur.

  As described above, the dispersion term δP and the hydrogen bond term δH in the Hansen solubility parameter are selected and combined with the solvents (B) and (C) having a specific range and a specific boiling point, thereby reducing the residual solvent, It is possible to uniformly dry the entire surface of the applied ink. In particular, in the ink of the present invention using a light-emitting material, if the above conditions are not satisfied, reduction of the light-emitting efficiency in the light-emitting layer due to the residual solvent and uneven brightness in the light-emitting layer due to in-plane uneven drying may occur. Absent.

  The ink for forming a functional layer of the present invention can be applied to a known and commonly used printing method or coating method. Specifically, for example, an offset printing method, a gravure printing method, a flexographic printing method, a screen printing method, a reverse printing method, a depenser printing method, an inkjet printing method, a microcontact printing method, and the like can be given. Above all, it is preferable to apply the method to the ink jet printing method since only a necessary amount of ink can be applied to a fine region and there is no waste of ink.

  The viscosity of the ink solvent containing the solvent (B) and the solvent (C) is not particularly limited, but is preferably 0 to 6.0 mPa · s, and is preferably 1.2 to 5.0 mPa · s. More preferably, it is particularly preferably 1.5 to 4.5 mPa · s. When the viscosity of the solvent is 1.0 mPa · s or more, when the ink of the present invention is ejected by an inkjet method to form a coating film with ink droplets, nozzle clogging of the inkjet head is less likely to occur. preferable. On the other hand, when the viscosity of the solvent is 6.0 mPa · s or less, the viscosity of the obtained ink does not become excessively high, so that it is easy to discharge fine droplets of the ink from the inkjet head, which is preferable.

  The surface tension of the solvent is preferably from 20 to 45 mN / m, more preferably from 25 to 43 mN / m, and particularly preferably from 28 to 40 mN / m. When the surface tension of the ink is 20 mN / m or more, when the ink of the present invention is ejected by the ink jet method, the wettability of the ink on the nozzle surface does not become excessively high, and the ink adheres around the nozzle. This is preferable because the flight direction of the droplets is less likely to bend. On the other hand, when the surface tension of the ink is 45 mN / m or less, it is preferable because the shape of the meniscus at the nozzle tip is easily stabilized, and the control of the ink discharge amount and the discharge timing can be facilitated.

[Additive]
The functional layer forming ink of the present invention may contain known and commonly used additives as necessary. When preparing an ink composition for an organic light emitting device, additives such as a leveling agent and a viscosity adjusting agent are used as necessary for the purpose of improving ink jet ejection properties or improving the smoothness when drying the ink jet ejection material. May be contained.

[Leveling agent]
The leveling agent is not particularly limited, but a silicone compound, a fluorine compound, a siloxane compound, a nonionic surfactant, an ionic surfactant, a titanate coupling agent, or the like can be used. Of these, silicone compounds and fluorine compounds are preferred.

  The silicone compound is not particularly limited, and examples thereof include dimethyl silicone, methyl silicone, phenyl silicone, methylphenyl silicone, alkyl-modified silicone, alkoxy-modified silicone, and polyether-modified silicone. Of these, dimethyl silicone and methyl phenyl silicone are preferred.

  Examples of the fluorine-based compound include, but not particularly limited to, polytetrafluoroethylene, polyvinylidene fluoride, fluoroalkyl methacrylate, perfluoropolyether, and perfluoroalkylethylene oxide. Of these, polytetrafluoroethylene is preferred.

  The siloxane compound is not particularly limited, and examples thereof include a dimethylsiloxane compound (trade names: KF96L-1, KF96L-5, KF96L-10, KF96L-100, manufactured by Shin-Etsu Silicone Co., Ltd.).

  Among the above-mentioned leveling agents, it is preferable to use a silicone compound, a fluorine compound, or a siloxane compound, and it is more preferable to use a siloxane compound.

  The above-mentioned leveling agents may be used alone or in combination of two or more.

  The addition rate of the leveling agent varies depending on the desired performance, but is preferably 0.001 to 5% by mass, and more preferably 0.001 to 1% by mass, based on the total mass of the ink composition for an organic light emitting device. Is more preferable. It is preferable that the addition rate of the leveling agent is 0.001% by mass or more because the smoothness of the coating film can be improved. On the other hand, when the addition rate of the leveling agent is 5% by mass or less, it is preferable because the luminous efficiency can be improved.

[Viscosity modifier]
Examples of the viscosity modifier include, but are not particularly limited to, poly (α-methylstyrene), polystyrene, styrene / acrylonitrile copolymer, styrene / butadiene / acrylonitrile copolymer, polymethyl methacrylate, methacryl / styrene copolymer, polycarbonate, and the like. Can be used. Of these, poly (α-methylstyrene), polystyrene, styrene / acrylonitrile copolymer, styrene / butadiene / acrylonitrile copolymer, and polymethyl methacrylate are preferred.

  The above-mentioned viscosity modifiers may be used alone or in combination of two or more.

  The addition rate of the viscosity modifier varies depending on the desired performance, but is preferably from 0.001 to 5% by mass, and more preferably from 0.01 to 1% by mass, based on the total mass of the light emitting element ink composition. Is more preferable. When the addition ratio of the viscosity modifier is 0.001% by mass or more, it is preferable because aggregation of the light emitting host material can be suppressed and luminous efficiency can be improved. On the other hand, when the addition rate of the viscosity modifier is 5% by mass or less, it is preferable because the flying shape of the ink jet droplet can be improved.

  When the functional material (A) as the ink for forming a functional layer of the present invention is likely to be deactivated by oxygen, water, or the like and not function stably for a long period of time, the ink is dissolved in the preparation of the ink. After using solvents (B) and (C) from which gases and moisture have been removed as much as possible, or after preparing ink, the ink is degassed or saturated or supersaturated with an inert gas, heated or passed through a desiccant. It is preferable to remove dissolved oxygen and water as much as possible, such as by dehydration.

  In addition, metal ions and halogen ions are repeatedly washed or removed through an ion exchange resin, and foreign substances having a large particle diameter are filtered. For example, the ink for forming a functional layer of the present invention is applied to an ink jet printing method. It is preferable to use it because higher reliability can be ensured also from the viewpoint of nozzle clogging and long-term continuous printability.

[Organic light emitting device]
When an ink composition for an organic light emitting device is prepared as one embodiment of the ink for forming a functional layer of the present invention, an organic light emitting device can be provided based on the composition. In this case, the organic light emitting device includes at least an anode, a light emitting layer, and a cathode. Note that the organic light emitting device may include one or more other layers such as a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer. Further, a known member such as a sealing member may be included.

  Hereinafter, each configuration of the light emitting element will be described in detail.

[anode]
The anode is not particularly limited, but may be a metal such as gold (Au), copper iodide (CuI), indium tin oxide (ITO), tin oxide (SnO ₂ ), zinc oxide (ZnO), or the like. These materials may be used alone or in combination of two or more.

  The thickness of the anode is not particularly limited, but is preferably from 10 to 1000 nm, and more preferably from 10 to 200 nm.

  The anode can be formed by a method such as vapor deposition or sputtering. At this time, the pattern may be formed by a photolithography method or a method using a mask.

[Hole injection layer]
The hole injection layer is an optional component in the light emitting element and has a function of taking in holes from the anode. Usually, holes taken from the anode are transported to the hole transport layer or the light emitting layer.

  The hole injecting material is not particularly limited, but a phthalocyanine compound such as copper phthalocyanine; a triphenylamine derivative such as 4,4 ′, 4 ″ -tris [phenyl (m-tolyl) amino] triphenylamine; Cyano compounds such as 5,5,8,9,12-hexaazatriphenylenehexacarbonitrile and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane; vanadium oxide, molybdenum oxide and the like Oxide; amorphous carbon; conductive polymers such as polyaniline (emeraldine), poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonic acid) (PEDOT-PSS), and polypyrrole. The hole injecting material is preferably a conductive polymer, and PEDOT-PSS. More preferably.

  The thickness of the hole injection layer is not particularly limited, but is preferably 0.1 nm to 5 μm.

  The hole injection layer may be a single layer or a laminate of two or more layers.

[Hole transport layer]
The hole transport layer is an arbitrary component in the light emitting element and has a function of efficiently transporting holes. In addition, the hole transport layer can have a function of preventing hole transport. The hole transport layer usually takes in holes from the anode or the hole injection layer and transports holes to the light emitting layer.

  The hole transporting material that can be used for the hole transporting layer is not particularly limited, but TPD (N, N′-diphenyl-N, N′-di (3-methylphenyl) -1,1′-biphenyl-4) , 4 ′ diamine), α-NPD (4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl), m-MTDATA (4,4 ′, 4 ″ -tris (3-methyl Low molecular triphenylamine derivatives such as phenylphenylamino) triphenylamine; and high molecular compounds such as diamine polymers obtained by polymerizing polyvinyl carbazole and triarylamine derivatives by introducing substituents. The transporting material is preferably a polymer compound obtained by introducing a substituent into a triphenylamine derivative or a triarylamine derivative, and has a fluorene skeleton. And more preferably the diamine polymer that.

  The thickness of the hole transport layer is not particularly limited, but is preferably 1 nm to 5 μm, more preferably 5 nm to 1 μm, and further preferably 10 to 500 nm.

[Light-emitting layer]
The light emitting layer has a function of emitting light using energy generated by recombination of holes and electrons injected into the light emitting layer.

  At this time, the light emitting layer contains a known and commonly used material such as the light emitting material and the host material as the functional material (A).

  The thickness of the light emitting layer is not particularly limited, but is preferably 2 nm to 30 μm, more preferably 10 nm to 20 μm, further preferably 15 nm to 15 μm, and particularly preferably 15 to 200 nm. preferable. The above range is preferable because the film thickness can be controlled with high accuracy.

[Electron transport layer]
The electron transport layer is an optional component in the organic light emitting device and has a function of efficiently transporting electrons. In addition, the electron transport layer can have a function of preventing electron transport. The electron transport layer usually takes in electrons from the cathode or the electron injection layer and transports the electrons to the light emitting layer.

  The electron transporting material that can be used for the electron transporting layer is not particularly limited, but tris (8-quinolylate) aluminum (Alq), tris (4-methyl-8-quinolinolate) aluminum (Almq3), bis (10-hydroxybenzoyl) [H] Quinolinato) beryllium (BeBq2), bis (2-methyl-8-quinolinolato) (p-phenylphenolato) aluminum (BAlq), bis (8-quinolinolato) zinc (Znq), 8-hydroxyquinolinolatolithium A metal complex having a quinoline skeleton or a benzoquinoline skeleton such as (Liq); a metal complex having a benzoxazoline skeleton such as bis [2- (2′-hydroxyphenyl) benzoxazolate] zinc (Zn (BOX) 2); Bis [2- (2'-hydroxyphenyl) benzo Azolate] zinc (Zn (BTZ) 2) metal complex having a benzothiazoline skeleton; 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (PBD); 3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole (TAZ), 1,3-bis [5- (p-tert-butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (OXD-7), 9- [4- (5-phenyl-1,3,4-oxadiazol-2-yl) phenyl] carbazole ( CO11), 2,2 ′, 2 ″-(1,3,5-benzenetriyl) tris (1-phenyl-1H-benzimidazole) (TPBI), 2- [3- (dibenzothiophen-4-yl) ) Phenyl] -1-phenyl-1H-benzimidazole (mDBTBIm-II) and the like; benzimidazole derivative; quinoline derivative; perylene derivative; pyridine derivative; pyrimidine derivative; triazine derivative; quinoxaline derivative; diphenylquinone derivative; Derivatives and the like. Among these, the electron transporting material is preferably a benzimidazole derivative, a pyridine derivative, a pyrimidine derivative, a triazine derivative, or a phenanthroline derivative.

  The above-mentioned electron transport materials may be used alone or in combination of two or more.

  The thickness of the electron transporting layer is not particularly limited, but is preferably 5 nm to 5 μm, and more preferably 5 to 200 nm.

  The electron transport layer may be a single layer or a laminate of two or more layers.

[Electron injection layer]
The electron injection layer is an optional component in the organic light emitting device and has a function of taking in electrons from a cathode. Usually, electrons taken from the cathode are transported to the electron transport layer or the light emitting layer.

  The electron injecting material that can be used for the electron injecting layer is not particularly limited, but includes alkali metals such as lithium and calcium; metals such as strontium and aluminum; alkali metal salts such as lithium fluoride and sodium fluoride; 8-hydroxyquino Alkali metal compounds such as lithium lithium; alkaline earth metal salts such as magnesium fluoride; oxides such as aluminum oxide; Among these, the electron injection material is preferably an alkali metal, an alkali metal salt, or an alkali metal compound, and more preferably an alkali metal salt or an alkali metal compound.

  The above electron injecting materials may be used alone or in combination of two or more.

  The thickness of the electron injection layer is not particularly limited, but is preferably from 0.1 nm to 5 μm.

  The electron injection layer may be a single layer or a laminate of two or more layers.

[cathode]
As the cathode is not particularly limited, lithium, sodium, magnesium, aluminum, sodium - potassium alloy, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al 2 _{O 3)} mixture and rare earth metal . These materials may be used alone or in combination of two or more.

  The cathode can be usually formed by a method such as vapor deposition or sputtering.

  The thickness of the cathode is not particularly limited, but is preferably from 10 to 1,000 nm, more preferably from 10 to 200 nm.

<Manufacturing method of organic light emitting device>
According to one embodiment of the present invention, a method for manufacturing an organic light emitting device is provided. The method for producing an organic light-emitting element includes: using a light-emitting material as a functional material, forming an ink for forming a functional layer prepared to have a viscosity and a surface tension suitable for the above-described ink-jet printing method, using an ink composition for an organic light-emitting element. A step of forming a light-emitting layer by applying it on a support by an inkjet printing method (hereinafter, also referred to as a “light-emitting layer forming step”).

[Light emitting layer forming step]
The light emitting layer forming step is a step of applying the ink composition for an organic light emitting element on a support by an ink jet method to form a light emitting layer.

  Hereinafter, a light emitting layer forming step in one embodiment will be described with reference to the drawings.

  More specifically, FIG. 1 is a partial cross-sectional view schematically showing a step of forming a coating film by an inkjet method. FIG. 1 includes a substrate 1, an anode 2 disposed on the substrate, and a hole transport layer 4 disposed on the anode. At this time, the stacked body of the anode 2 and the hole transport layer 3 having a plurality on the substrate is separated by the bank 3. When the ink composition for an organic light emitting device is ejected from the nozzle 6 of the inkjet head 7, a coating film 5 of the ink composition for an organic light emitting device is formed on the hole transport layer 3. By drying the obtained coating film, a light emitting layer can be formed.

<Ink composition for organic light emitting device>
As the ink composition for an organic light emitting device, the above-described ones can be used, and thus the description is omitted here.

[Support]
The support is a constituent layer of the organic light emitting device adjacent to the light emitting layer, and differs depending on the organic light emitting device to be manufactured. For example, when manufacturing an organic light emitting device comprising an anode, a light emitting layer and a cathode, the support is the anode or the cathode. When manufacturing an organic light-emitting device comprising an anode, a hole injection layer, a light-emitting layer, an electron injection layer, and a cathode, the support is a hole injection layer or an electron transport layer. Thus, the support is an anode, a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, or a cathode, preferably an anode, a hole injection layer, a hole transport layer, More preferably, it is a hole injection layer or a hole transport layer, and further preferably, it is a hole transport layer.

  Note that a bank may be formed on the support. With the bank, a light-emitting layer can be formed only at a desired position.

  The height of the bank is preferably 0.1 to 5.0 μm, more preferably 0.2 to 3.0 μm, and even more preferably 0.2 to 2.0 μm.

  Further, the width of the bank opening is preferably 10 to 200 μm, more preferably 30 to 200 μm, and further preferably 50 to 100 μm.

  Further, the length of the bank opening is preferably from 10 to 400 μm, more preferably from 20 to 200 μm, and even more preferably from 50 to 200 μm.

  Further, the taper angle of the bank is preferably from 10 to 100 degrees, more preferably from 10 to 90 degrees, and further preferably from 10 to 80 degrees.

[Application]
The application is performed by, for example, an inkjet printing method. More specifically, the ink composition for an organic light emitting device is discharged from a nozzle of an inkjet head to a support.

  At this time, the discharge amount of the ink composition for an organic light emitting device is preferably 1 to 50 pL / time, more preferably 1 to 30 pL / time, and still more preferably 1 to 20 pL / time.

  The opening diameter of the inkjet head is preferably from 5 to 50 μm, and more preferably from 10 to 30 μm, from the viewpoint of nozzle clogging and ejection accuracy.

  The temperature at the time of forming the coating film is not particularly limited, but from the viewpoint of suppressing crystallization of the luminescent material (host material and / or luminescent material) contained in the ink composition for an organic light emitting device, from 10 to 50 ° C. Is preferably 15 to 40 ° C, more preferably 15 to 30 ° C.

  Although the relative humidity at the time of forming a coating film is not particularly limited, it is preferably 0.01 ppm to 80%, more preferably 0.05 ppm to 60%, and preferably 0.1 ppm to 15%. More preferably, it is 1 ppm to 1%, particularly preferably, 5 to 100 ppm. When the relative humidity is 0.01 ppm or more, it is preferable because conditions for forming a coating film can be easily controlled. On the other hand, when the relative humidity is 80% or less, it is preferable because the amount of water adsorbed on the coating film which can affect the obtained light emitting layer can be reduced.

[Dry]
By drying the obtained coating film, a light emitting layer can be formed.

  The drying temperature is not particularly limited, but may be left at room temperature (25 ° C.) or may be heated. When the heating is performed, the temperature is preferably 40 to 130 ° C, more preferably 40 to 80 ° C.

  The drying pressure is preferably performed under reduced pressure, more preferably under reduced pressure of 0.001 to 100 Pa.

  Further, the drying time is preferably from 1 to 90 minutes, more preferably from 1 to 30 minutes.

[Steps of Forming Other Layers]
Other layers constituting the organic light emitting device, specifically, the anode, the hole injection layer, the hole transport layer, the electron transport layer, the electron injection layer, and the cathode can be appropriately formed by a known method. .

  For example, the anode and the cathode can be formed by a method such as evaporation or sputtering.

  Further, the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer can be formed by a vacuum evaporation method, a spin coating method, a casting method, an inkjet method, an LB method, or the like.

  When the ink for forming a functional layer of the present invention is used, by selecting and using a more suitable solvent (B), all the pixels are dried equally regardless of the substrate position, and the coating in the pixels is performed. A remarkably excellent technical effect that the film is flattened is obtained. Even if the drying unevenness between the pixels is solved, the coating smoothness in the pixel may be low. However, such a disadvantage is solved by the optimal ink of the present invention.

  In particular, when a functional layer such as a light emitting layer of an organic light emitting element is formed, the ink discharged to the pixels located at the side edges of the substrate dries faster than the ink discharged to the pixels located at the center of the substrate. Tend to. This is because, in the center of the substrate, there are many ink solvent molecules that evaporate because each pixel is adjacent to each other, but the pixels located around the side edge of the ejection substrate have few ink solvent molecules that evaporate. This is because evaporation becomes faster than in the center. If the drying time varies depending on the pixel position in the substrate as described above, unevenness in the thickness of the light emitting layer occurs between pixels in the substrate. When there is such film thickness unevenness, a difference occurs in the current flowing through the light emitting layer and the like, which causes display unevenness such as uneven brightness and uneven emission color when the light emitting layer emits light.

  Therefore, dummy pixels having substantially the same area as the pixels located on the ejection substrate and not contributing to the display are arranged around the display region, and the ink containing the constituent material of the light emitting layer formed on the pixels located on the ejection substrate is used as the ink. A configuration has been proposed in which dummy pixels are arranged to prevent or suppress the occurrence of unevenness in the thickness of a light-emitting layer or the like at the center and side edges of the discharge substrate.

  In addition, in order to enhance the effect of preventing and suppressing the unevenness in the thickness of the light emitting layer due to the arrangement of the dummy pixels, the amount of the solvent per unit area discharged to the dummy pixels is determined by the amount of the solvent per unit area discharged to the pixels in the display area. It has been proposed to increase the amount of ink per unit area to be ejected to dummy pixels or to be equal to or more than the amount of ink per unit area to be ejected to pixels of an ejection substrate.

  On the other hand, as a method of preventing unevenness in the thickness of the light emitting layer or the like by devising a drying method using a drying device, a region where the ink is disposed on the substrate is divided into a plurality of regions, and an exhaust amount for each of the divided regions is independently controlled. There is also a proposal of a drying device provided with a member which can be controlled by heating, and a proposal of a drying device for drying by making the temperature distribution of the substrate uniform using a current plate or a heater.

  When the ink for forming a functional layer of the present invention is used for the purpose of forming the light emitting layer of such an organic light emitting element, the dummy pixels are intentionally formed as described above, or the amount of ink and the drying conditions are controlled by the area. A dry film that is uniform over the entire display area, both outside the pixel and inside the pixel, without using special conditions and devices such as changing each time, or without the trouble of adjustment. Since a light-emitting layer having extremely small thickness unevenness can be obtained, a highly reliable display device having no display unevenness can be easily obtained.

  Hereinafter, the present invention will be described using examples, but the present invention is not limited to the description of the examples.

[substrate]
Ink was ejected by an inkjet printing method onto a substrate having a length of 4 cm and a width of 7 cm having pixels of 300 μm in length and 100 μm in width. In this substrate, the pixel located at the lower right was defined as a side edge pixel, and the pixel located at the center of the substrate was defined as a center pixel.

[Preparation of functional layer forming ink]
First, tris [2- (p-tolyl) pyridine] iridium (Ir (mppy) ₃ ) (manufactured by Lumtec), 9,9 ′-(p-tert-butylphenyl) -1,3-bis Carbazole H-1 (manufactured by DIC Corporation) was prepared and dissolved in a solvent such that the content of each was 1.5% by mass. Ink compositions were prepared (Examples 1 to 16, Comparative Examples 1 to 5). See Tables 1 and 2.

  In preparing these inks, diphenyl ether, 3-phenoxytoluene, 1-methoxynaphthalene, and 2-methoxybiphenyl were prepared as the solvent (B). On the other hand, cyclohexylbenzene was prepared as the solvent (C). The boiling points, δP and δH of the various solvents used are shown in Tables 1-2. Although 1-methylnaphthalene has a boiling point outside the range of the solvent (B) of the present invention, it is shown in Table 2 in the column of the solvent (B) for convenience. These were combined and used as a solvent or a dispersion medium so as to have a mass ratio as shown in Tables 1 and 2.

<Production of light emitting device>
An organic light emitting device was manufactured as described below. In adopting the ink jet printing method, ink is discharged using a printer DMP2831 and a cartridge box DMC-11610 (manufactured by FUJIFILM Corporation) under conditions of a discharge amount of pl order, an operating temperature of 25 ° C., and a relative humidity of 50%. I made it.

1) An ITO (indium tin oxide) substrate having a bank structure was washed with acetone and propanol in this order, and then irradiated with UV / O ₃ .
2) Poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonic acid) (PEDOT-PSS resin. CLEVIOS P JET NV2, Heraeus) is formed into a film having a thickness of 45 nm by discharging ink from an inkjet printer. Then, the mixture was heated at 180 ° C. for 15 minutes in the atmosphere to form a hole injection layer.
3) Next, a 1% by weight tetralin solution of HT-2 (American Dye Source) represented by the following formula was discharged onto the hole injection layer by an ink jet printer to form a film having a thickness of 30 nm, and a nitrogen atmosphere was formed. The hole transport layer was formed by drying at 200 ° C. for 30 minutes.
4) The light emitting layer forming inks of the respective organic light emitting elements of the examples and the comparative examples prepared above were discharged onto the hole transport layer by an ink jet printer to form a film having a thickness of 30 nm. The light emitting layer was formed by drying in an atmosphere at 25 ° C. under a vacuum condition of 0.003 Pa for 40 minutes.
5) Under a vacuum condition of 0.005 Pa, ET-1 represented by the following formula as an electron transport layer is 45 nm, lithium fluoride is 0.5 nm as an electron injection layer, and aluminum is 100 nm as a cathode. A film was formed.
6) Finally, the substrate was transported to a glove box and sealed with a glass substrate to produce an organic light emitting device.

<Evaluation of luminance difference between pixels>
A current of 10 mA / cm2 was applied to the obtained light emitting device to emit light. At this time, the luminance of the ten pixels at the panel side end and the luminance of the ten pixels at the center of the panel were measured using a luminance meter (Topcon BM-9). The average of the brightness at the side edge and the center was taken and evaluated according to the following criteria.

Luminance difference index = (average luminance of pixel at side edge / average luminance of pixel at center) × 100
4: Luminance difference index is 80 or more
3: Brightness difference index is 70 or more and less than 80
2: Luminance difference index is 60 or more and less than 70
1: Luminance difference index is less than 60

<Emission efficiency evaluation>
A current of 10 mA / cm2 was applied to the obtained light emitting device to emit light. At this time, the luminous efficiency of 20 pixels at the center of the panel was measured with a luminance meter (Topcon BM-9), and the luminous efficiency was evaluated according to the following criteria.

The luminous efficiency of the device obtained in Comparative Example 5 was set to 1.0, and the luminous efficiencies of the light-emitting devices obtained in other than Comparative Example 5 were determined as relative values, and this was used as a measure of the luminous efficiency. The higher the numerical value, the higher the luminous efficiency.

3: Relative luminous efficiency is less than 1.2
2: Relative luminous efficiency is 1.1 or more and less than 1.2
1: Relative luminous efficiency is less than 1.1

  The results obtained by the above evaluation are shown in Tables 1 and 2 below. In the table, the boiling point is the boiling point of the solvent at atmospheric pressure, δP and δH are the values of the respective Hansen solubility parameters of the solvent, and the ratio is one of the solvents when the sum of two different solvents is 100 parts by mass conversion. Are respectively shown.

  As can be seen from the comparison between Examples 1 to 4 and Comparative Example 1 and the comparison between Examples 5 to 8 and Comparative Example 2 in Table 1, even if the inks were obtained by using the same solvent in combination, It is clear that the technical effect of the present invention is exerted only at a specific mixing ratio when the mixing ratio is different, and the luminance difference and the luminance change greatly. Comparative Example 2 is an experimental example corresponding to Patent Document 2 cited as the above-mentioned prior art document. From a comparison between Example 8 and Comparative Example 2, even when the solvent (B) or the solvent (C) is used, It can be seen that there is a range of the combination ratio where the technical effect of the present invention is not exhibited depending on the ratio. It is also apparent from the comparison between Examples 1 and 2 or the comparison between Examples 5 and 6 that the degree of this technical effect differs when the combination ratio is different. In particular, this difference is more remarkable in luminance difference than luminous efficiency.

  In addition, comparing Examples 1 to 8, Examples 9 to 12, and Examples 13 to 16, the technical effects of the naphthalene skeleton or the biphenyl skeleton compound are superior to the diphenyl ether skeleton compound in terms of both luminance difference and luminous efficiency. It can be seen that the range of the more excellent combination ratio is wider. This is presumably because the naphthalene skeleton or biphenyl skeleton compound has higher solubility of the functional material than the phenyl ether skeleton compound. When the solubility of the solvent was high, the effect of stably dissolving the solute and preventing precipitation as crystals even when the solvent was extremely small during drying was confirmed.

  Comparative Example 5 is an experimental example corresponding to Patent Document 1 cited as the above-mentioned prior art document. As can be seen from a comparison between Example 15 and Comparative Example 5, the mixing ratio of the solvent is the same and the chemical structure of the solvent (B) is the same. Are similar (both have a naphthalene skeleton), but the effects on luminance difference and luminous efficiency are greatly different. This cannot be expected from the common knowledge of those skilled in the art that estimates the technical effects of the invention from the chemical structure of the solvent used. This is presumably because the boiling point of 1-methylnaphthalene of Comparative Example 5 was too low, so that the end on the panel side dried extremely fast, causing drying unevenness. In addition, it is presumed that the solute is likely to precipitate as crystals due to rapid drying, and the luminous efficiency is lowered.

1: substrate 2: anode 3: bank 4: hole transport layer 5: coating film 6: nozzle 7: inkjet head.

Claims (5)

In a functional layer forming ink containing a functional material (A) and at least a first solvent or dispersion medium (B) and a second solvent or dispersion medium (C),
1) Both the solvents or dispersion media (B) and (C) have Hansen solubility parameters δP <10 and δH <9,
2) the first solvent or dispersion medium (B) is a solvent or dispersion medium containing an aromatic ring and having a boiling point of 250 to 310 ° C. at normal pressure;
3) The second solvent or the dispersion medium (C) is a solvent or a dispersion medium having a boiling point at normal pressure of 160 ° C. to the boiling point of the first solvent or the dispersion medium (B) used in 1 above,
4) When the total used amount of the first solvent or the dispersion medium (B) and the second solvent or the dispersion medium (C) is 100 parts by mass conversion, the second solvent or the dispersion medium (C) It was used so as to exceed the same amount as the amount of one solvent or dispersion medium (B),
An ink for forming a functional layer, comprising:   The first solvent or the dispersion medium (B) is diphenyl ether, 1-ethylnaphthalene, 2-isopropylnaphthalene, 1-methoxynaphthalene, 3-phenoxytoluene, 2-methoxybiphenyl, 2-ethoxynaphthalene, 1-ethoxynaphthalene, The functional layer forming ink according to claim 1, which is at least one kind of solvent or dispersion medium selected from the group consisting of 3,3'-dimethylbiphenyl, 3-ethylbiphenyl and 4-isopropylbiphenyl.   The ink for forming a functional layer according to claim 1 or 2, wherein the second solvent or dispersion medium (C) is at least one solvent or dispersion medium selected from the group consisting of ethyl benzoate and cyclohexylbenzene.   When the total used amount of the first solvent or the dispersion medium (B) and the second solvent or the dispersion medium (C) is 100 parts by mass, 50 parts of the second solvent or the dispersion medium (C) is used. The functional layer forming ink according to any one of claims 1 to 3, wherein   The functional layer forming ink according to any one of claims 1 to 4, wherein the functional material (A) is a light emitting material.

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